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a good many magnetic tapes may turn into pumpkins at midnight on 9 September 1999. Where valid date ranges were ignored, the date may be "99/99/99," which may expire on 1 January 2000. |
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For many systems in the financial sector, the software looks ahead one year. Such software will begin generating invalid dates, and possibly crashing systems, as early as 1 January 1999. |
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Dates in keys A special problem is the matter of dates used as keys in indexed files. This is a rather common application. Where the date contains a two-digit year and applications depend upon the records in the file being accessible in chronological order, a definite problem exists. |
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1.8.2
A.D. 2000 in the Western Calendar |
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In this section, I take a quick look at some aspects of the year A.D. 2000. |
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First of all, it should be pointed out that A.D. 2000 is not the start of a new millennium. The system used for numbering calendar years starts with the year 1, not 0. Thus, the first century contains the years A.D. 1 through A.D. 100, and the second century begins with A.D. 101. Each century thus begins with a year ending in "1," not "0." The third millennium starts on 1 January 2001. |
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Regardless of the mindless hoopla surrounding the year 2000, the millennium celebration will occur one year too early. |
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The year A.D. 2000 is far more interesting from the perspective of the Gregorian leap year rule. The rule has three parts. The first part specifies that years evenly divisible by four are leap years. Most people live their entire lives experiencing only the regular pattern of leap years every four years. |
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Only once in a century is the second part of the Gregorian leap year rule exercised. By this rule, years that are also evenly divisible by 100 are designated as common years, rather than leap years. Thus, the year 1900 was not a leap year, even though the number 1900 is evenly divisible by four, because the second rule takes precedence over the first. A small minority of people experience this second rule. |
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The third part of the rule introduces yet another reversal, declaring that years also evenly divisible by 400 are leap years, after all. This rule takes precedence over the second rule. |
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